Optical heterodyne detection pulse receiving system and method

Abstract

An optical heterodyne detection pulse receiving system operates such that the light from a local oscillator and from a pulse modulated optical carrier are mixed, and a signal having an intermediate (difference) frequency is extracted. Pulse signal regeneration is effected by demodulating the intermediate frequency signal while maintaining a positive integer multiple of one-half the intermediate frequency signal synchronized with the repeating frequency of the pulse signal.

What is claimed is: 
     
       1. An optical heterodyne detection pulse receiving method comprising the steps of: mixing an optical carrier modulated with a pulse signal and a local oscillator light wave having a frequency different from said carrier, and producing an electrical signal having an intermediate frequency equal to the difference between the frequency of said local oscillator light wave and that of said optical carrier;   extracting the timing signal of said pulse signal from said electrical signal;   generating a reproduction of said pulse signal by demodulating said electrical signal; and   controlling the frequency of said local oscillator light wave so as to synchronize a first signal, derived from said electrical signal and having a period which is an integer multiple of the half period of said electrical signal, with a second signal derived from said timing signal and having a period equal to that of said pulse signal.   
     
     
       2. The optical heterodyne detection pulse receiving method, as claimed in claim 1, wherein said optical carrier modulated with a pulse signal is a pulse phase-modulated optical carrier. 
     
     
       3. The optical heterodyne detection pulse receiving method, as claimed in claim 1, wherein said optical carrier modulated with a pulse signal is a pulse amplitude-modulated optical carrier. 
     
     
       4. An optical heterodyne detection pulse receiving system comprising: an input laser light wave modulated with a pulse signal;   local oscillator means for generating a local laser light wave having a frequency different from that of said input laser light wave;   means for aligning wave fronts of the local laser light wave and said input laser light wave;   means for receiving said local laser light wave and said input laser light wave, and for generating an electrical signal,   timing means for extracting a timing signal of said pulse signal from said electrical signal;   means for extracting from said electrical signal an intermediate frequency signal equivalent to the frequency difference between said local laser light wave and said input laser light wave; and   means for controlling said local oscillator means so as to synchronize a first signal derived from said intermediate frequency signal and having a period of a multiple N (N being a positive integer) of the half period of said intermediate frequency signal with a second signal derived from said timing signal and having a period equal to that of said pulse signal.   
     
     
       5. The optical heterodyne detection pulse receiving system, as claimed in claim 4, wherein said modulated light wave is pulse amplitude-modulated with said pulse signal. 
     
     
       6. The optical heterodyne detection pulse receiving system, as claimed in claim 4, wherein said modulated light wave is pulse phase-modulated with said pulse signal. 
     
     
       7. The optical heterodyne detection pulse receiving system as claimed in claim 4, wherein said local laser light wave receiving, electrical signal generating means comprises a photoelectric conversion device. 
     
     
       8. The optical heterodyne detection pulse receiving system as claimed in claim 4, further comprising an intermediate frequency amplifier between said local laser light wave receiving, electrical signal generating means and said intermediate frequency signal extracting means. 
     
     
       9. The optical heterodyne detection pulse receiving system as claimed in claim 8, further including envelope detector means receiving an output of said intermediate frequency amplifier, and baseband amplifier means coupled between said envelope detector means and said timing means. 
     
     
       10. The optical heterodyne detection pulse receiving system as claimed in claim 9, further including original signal regenerating means receiving an output of said baseband amplifier and a synchronization timing pulse from said timing means. 
     
     
       11. The optical heterodyne detection pulse receiving system as claimed in claim 8, further including delay detector means receiving an output of said intermediate frequency amplifier, baseband amplifier means coupled between said delay detector means and said timing means, signal regenerator means receiving outputs of said timing means and said baseband amplifier means, pulse width share converter means coupled to an output of said signal regenerator means and receiving said timing means output, and code converter means coupled to an output of said pulse width share converter means. 
     
     
       12. The optical heterodyne detection pulse receiving system as claimed in claim 4, said controlling means varying a driving current supplied to said local oscillator means so as to vary an output frequency of said local oscillator means.